He argued that there is no reason there can’t be digital margin notes, and what’s more, there wouldn’t need to be just one copy of the margin notes:

Rather than there just being one copy of that famous person’s notes, why not offer them for sale to anyone else who buys the ebook? … The idea is for thought leaders, celebrities, etc., to make handwritten notes in ebooks they read, and sell them as an add-on.

A win-win-win for publishers, authors and readers. And as Bob Stein, founder and co-director of The Institute for the Future of the Book, pointed out in an e-mail interview, people are already experimenting:

Marginalia is alive and well in the digital era. Check out the complex discussion conducted by seven women over the course of six weeks in the margin of Doris Lessing’s “The Golden Notebook.”

There are experiments in academia as well. It’s only a matter of time before marginalia processes develop into a form suitable for mainstream digital books.